Wireless Energy Transfer In A Multipath Environment

ABSTRACT

A method for wireless energy transfer in a multipath environment includes transmitting a first energy beam with a first one of a plurality of Power Access Points (PAPs). A second energy beam is transmitted with a second PAP. A reflected beam is formed by the first energy beam reflecting from a reflective surface, wherein the first energy beam constructively interferes with the second energy beam and the reflected beam to form at least one energy bubble. A location of the at least one energy bubble is changed with a control module by adjusting a relative phase between the first energy beam and the second energy beam, wherein the location is sequentially changed to a new location to cover a space including at least one energizable device, and the energy bubble comprises an energy level enabling the energizable device to transmit a reply signal to the first PAP.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a utility application claiming priority toco-pending U.S. patent application Ser. No. 15/424,752, filed on Feb. 3,2017, entitled, “IMPROVED WIRELESS ENERGY TRANSFER USING ALIGNMENT OFELECTROMAGNETIC WAVES,” which claims priority to U.S. ProvisionalApplication Ser. No. 62/292,926 filed on Feb. 9, 2016 entitled “PHASORDECOMPOSITION,” co-pending U.S. Provisional Application Ser. No.62/292,933 filed on Feb. 9, 2016 entitled “SWITCHED BEAM POLARIZATIONALIGNMENT,” co-pending U.S. Provisional Application Ser. No. 62/292,938filed on Feb. 9, 2016 entitled “RECEIVER LOCATION DETERMINATION,” and toco-pending U.S. patent application Ser. No. 14/923,847, filed on Oct.27, 2015, entitled, “WIRELESS ENERGY TRANSFER USING ALIGNMENT OFELECTROMAGNETIC WAVES,” which claims priority to U.S. ProvisionalApplication Ser. No. 62/073,448 filed on Oct. 31, 2014 entitled“DISTANCE WIRELESS CHARGING USING CHARGING STATIONS,” U.S. ProvisionalApplication Ser. No. 62/085,450 filed on Nov. 28, 2014 entitled“WIRELESS POWER TRANSFER AS APPLIED TO SOLAR PANELS,” U.S. ProvisionalApplication Ser. No. 62/129,325 filed on Mar. 6, 2015 entitled “WIRELESSPOWER TRANSFER USING ELECTROMAGNETIC WAVES ALIGNMENT,” and U.S.Provisional Application Ser. No. 62/136,142 filed on Mar. 20, 2015entitled “WIRELESS POWER TRANSMISSION,” the entireties of which areincorporated by reference herein.

FIELD

This disclosure relates generally to wireless energy transfer, and morespecifically to efficient systems and methods for the wireless transferof energy using alignment of electromagnetic waves.

BACKGROUND

Increased processing and connectivity capabilities of portable deviceshave resulted in a corresponding increase in the energy consumption ofthese devices. Furthermore, there are practical physical limits as tohow much energy a portable device can store, thus necessitating frequentcharging of these devices. Tethered solutions to powering portabledevices are limited in part due to a lack of standardization of theconnectors between the power cable and device, the weight andreliability of the charging cables, restrictions on the operatingenvironment (e.g., underwater or hazardous areas), and the generalconstraints on mobility that tethered solutions impose.

Wireless charging of portable devices, has previously been limited toshort distances (e.g. on the order of centimeters) by near-fieldtechniques such as inductive or capacitive coupling. Far-fieldtechniques that use lasers or microwave beams involve dangerously highpower levels, particularly in an environment including humans. Lasersand microwave beams are also typically limited to line-of-sightapplications.

Improvements in the capabilities of portable devices have also helpedenable an environment of an Internet of Things (IoT) wherein large anddense deployments of devices could collectively share information.However, previous solutions have been limited in their ability toefficiently power devices in an IoT environment, where the devicesrequire mobility, and have significantly different power consumptionrequirements. Similarly, increased usage of Radio FrequencyIdentification (RFID) tags requires an efficient way of powering devicesin a mobile environment without tethering, using dangerously high levelsof power, or imposing undue restrictions on the placement of chargingstations used to charge the RFID tags.

BRIEF SUMMARY

As will be appreciated, embodiments as disclosed herein include at leastthe following. In one embodiment, an apparatus for wireless energytransfer in a multipath environment comprises a first one of a pluralityof Power Access Points (PAPs) configured to transmit a first energybeam. A second PAP is configured to transmit a second energy beam. Areflected beam is formed by the first energy beam reflected from areflective surface, wherein the first energy beam constructivelyinterferes with the second energy beam and the reflected beam to form atleast one energy bubble. A control module is configured to sequentiallychange a location of the at least one energy bubble by adjusting arelative phase of the first energy beam and the second energy beam,wherein the location is sequentially changed to a new location to covera space including at least one energizable device, and the energy bubblecomprises an energy level enabling the at least one energizable deviceto transmit a reply signal to the first PAP.

Alternative embodiments of the apparatus for wireless energy transfer ina multipath environment include one of the following features, or anycombination thereof. The first energy beam and the second energy beameach comprise an omnidirectional pattern and two or more energy bubblesare formed. Two or more energizable devices comprising differentlocations are concurrently energized by a respective each energy bubble.A first phase of the first energy beam and a second phase of thereflected beam are aligned with the control module for an in-phasearrival at a first one of the at least one energizable device. A firstpolarity of the first energy beam and a second polarity of the secondenergy beam are aligned with the control module to have a same polarityrotation at a first one of the at least one energizable device. Thefirst energy beam has a first fundamental frequency equal to a secondfundamental frequency of the second energy beam. A first phase of thefirst energy beam, a second phase of the second energy beam, and a thirdphase of the reflected beam are aligned with the control module for anin-phase arrival at a first one of the at least one energizable device.A first polarity of the first energy beam, a second polarity of thesecond energy beam, and a third polarity of the reflected beam arealigned with the control module to have a same polarity rotation at afirst one of the at least one energizable device. The space is athree-dimensional space. The space comprises a warehouse environment.

In another embodiment, a method for wireless energy transfer in amultipath environment comprises transmitting a first energy beam with afirst one of a plurality of Power Access Points (PAPs). A second energybeam is transmitted with a second PAP. A reflected beam is formed by thefirst energy beam reflecting from a reflective surface, wherein thefirst energy beam constructively interferes with the second energy beamand the reflected beam to form at least one energy bubble. A location ofthe at least one energy bubble is changed with a control module byadjusting a relative phase of the first energy beam and the secondenergy beam, wherein the location is sequentially changed to a newlocation to cover a space including at least one energizable device, andthe energy bubble comprises an energy level enabling the energizabledevice to transmit a reply signal to the first PAP.

Alternative embodiments of the method for wireless energy transfer in amultipath environment include one of the following features, or anycombination thereof. Two or more energizable devices are energized by arespective energy bubble, wherein each of the two or more energizabledevices comprise a respective different location. A first phase of thefirst energy beam and a second phase of the second energy beam arealigned for an in-phase arrival at a first one of the at least oneenergizable device. A first polarity of the first energy beam and asecond polarity of the second energy beam are aligned to have a samepolarity rotation at a first one of the at least one energizable device.A first phase of the first energy beam, a second phase of the secondenergy beam and a third phase of the reflected beam are aligned for anin-phase arrival at a first one of the at least one energizable device.A first polarity of the first energy beam, a second polarity of thesecond energy beam and a third polarity of the reflected beam arealigned to have a same polarity rotation at a first one of the at leastone energizable device.

In another embodiment, a method for wireless energy transfer in amultipath environment comprises transmitting a first beam with a firstPower Access Point (PAP) and a second beam with a second PAP. Areflected beam is formed by the first energy beam reflecting from areflective surface, wherein the first energy beam and the second energybeam constructively interferes with the reflected beam to form aplurality of energy bubbles, and each energy bubble comprises an energylevel configured to enable at least one energizable device to transmit areply signal to the first PAP. A reply signal from at least oneenergizable device is received at the first PAP. A location of the atleast one energy bubble is changed with a control module by adjusting arelative phase between the first energy beam and the second energy beam,wherein the location is sequentially changed to a new location to covera three-dimensional space including at least one energizable device.

Alternative embodiments of the method for wireless energy transfer in amultipath environment include one of the following features, or anycombination thereof. Two or more energizable devices are energized by arespective energy bubble, wherein each of the two or more energizabledevices comprise a respective different location. A received energylevel of the respective two or more energizable devices is optimized bymaximizing a minimum Received Signal Strength Indication received at thefirst PAP from each of the energizable devices. The received energylevel is optimized using a phasor decomposition method

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is notlimited by the accompanying figures, in which like references indicatesimilar elements. Elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale.

FIG. 1 is a schematic view of an improved system for wireless energytransfer in accordance with an embodiment of the present disclosure.

FIG. 2 is a functional block diagram of a Control Module.

FIG. 3 is a graphical view of a sequence for adjusting phases of a PowerAccess Point.

FIG. 4 is a flowchart representation of pseudo-code for phasordecomposition.

FIG. 5 is a schematic view of an embodiment of a controllable slantlinear polarizer.

FIG. 6 is a schematic view of an embodiment for beam-steering usingswitched beams.

FIG. 7 is a flowchart representation of a method for generating aconnectivity map.

FIG. 8 is a flowchart representation of a method for improved wirelessenergy transfer in accordance with an embodiment of the presentdisclosure.

FIG. 9 is a flowchart representation of a method for improved wirelessenergy transfer in accordance with an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Embodiments of systems and methods described herein provide forimprovements to long-range wireless energy transfer from a plurality ofPower Access Points (PAPs), (also referred to as transmitters), to atleast one energizable device, (also referred to a Receiver of AppliedPower, or RAP). In one example, an energizable device is a RadioFrequency Identification (RFID) tag. A device is considered to beenergizable when it is capable of receiving radiated EM waves to provideenergy for device operation, from long-range wireless energy transfer.

In various embodiments, wireless energy transfer is realized over along-range, with low transmitted power, or both, by cohering thefrequency of multiple energy beams at a point on the energizable devicewhere energy is received (e.g., an antenna). The wireless energytransfer further includes at least one of cohering a phase and coheringa polarity of the energy beams. Various improvements to wireless energytransfer result from the teachings described herein, including one ofthe following improvements, or any combination thereof.

In various embodiments, the wireless energy transfer is improved byperforming phasor decomposition to rapidly determine the contributingamplitude, phase, and polarity from each PAP at each energizable device.Consequently, in some embodiments, the time required to cohere (e.g.,align) the frequency and at least one of the phase and the polarity ofthe energy beams to each other can be reduced by an order of 10,000resulting in real time energy beam alignment without requiringiteration. Real time energy beam alignment enables RFID tags to have“instant-on” performance and to remain powered at an optimal level asthe tags are moved. In one embodiment, the location of each tag istracked in real time as the tags are moved.

In other embodiments, the polarization alignment is performed with aswitched-beam selection rather than beam steering. Phased arrayapproaches perform faster beam steering, in excess of what is requiredfor power transfer applications, at the expense of increased cost andcomplexity. By using switched-beam selection for power transfer, thepower delivered by the PAPs is increased, and multipath issues arereduced.

In other embodiments, the wireless energy transfer is improved bydetermining the locations of multiple sensor tags, regardless of whethermulti-path distortions are present. A connectivity map is createdincluding the locations of RFID tags relative to RFID reference deviceswith predetermined locations. The connectivity map is determined bydetecting a change in a received signal level at a respective RFID tagilluminated by a scanned energy beam. Other methods are employed toimprove the resolution of the connectivity map, including selectivedeactivation of energy beams and rotating the polarity of the energybeams.

Referring to FIG. 1 an embodiment 10 of a system for wireless energytransfer provides energy (e.g. “powers”) an “Internet of Things” (IoT)12, including for example a cell phone 14 a, a tablet 14 b, a smartwatch 14 c, a stereo 14 d and a computer 14 e. The energizable devices14 a through 14 e (generally 14) are merely illustrative and should notbe considered to constrain the potential devices that would comprise theIoT 12. In one example, all of the devices 14 are of the same type. Inanother example, the devices 14 are low power devices such as RFID tags.In another example, the devices 14 are high power devices, such asmotorized wheelchairs. Various embodiments replace the IoT 12 with oneor more devices 14 that need not be associated with, nor communicate,with one another.

The devices 14 of the IoT 12 receive energy from a plurality of PAPs 16a, 16 b and 16 c (generally 16). Each PAP 16 a, 16 b and 16 c emits arespective energy beam 18 a, 18 b and 18 c (generally 18), wherein eachof the energy beams has at least one EM wave. Each of the EM waves of atleast two energy beams is directed (e.g. focused) at a receivinglocation of one of the devices 14 to optimize the energy received by theone device. By further aligning both the frequency and at least one ofthe phase and the polarity of each EM wave of each energy beam focusedat the receiving location, a coherent energy bubble 20 a is formed. Inthe context of this disclosure, references to aligning the frequency,phase or polarity of energy beams should be understood to mean aligning(or cohering) the EM waves within each energy beam and between energybeams.

For clarity of illustration, the coherent energy bubble 20 a in FIG. 1is shown adjacent to the IoT 12 environment, and formed by three energybeams 18. In practice, each coherent energy bubble is formed by at leasttwo energy beams and is focused at a point (e.g., a receiving antenna)on one of the devices 14 to maximize the received power by the onedevice. In one embodiment, more than one coherent energy bubble isformed, with each coherent energy bubble focused on a different device.In another embodiment, at least one coherent energy bubble istimed-shared between several devices.

The range 22 of the PAPs 16 to transmit a sufficient energy level to anenergizable device 14 depends in part on the required power that thedevice 14 needs to receive, the number of energy beams 18 used to formthe coherent energy bubble, limitations on the power of each of theenergy beams 18 (e.g. due to FCC limitations based on safe operatinglevels for living organisms), and the absorption characteristics of thetransmission medium through which the energy is transmitted.

In one embodiment, the energy delivered by each of the energy beams 18is adjusted by communication through a communication medium 24. Thecommunication medium 24 connects one or more devices 14 in the IoT 12over a path 28, to one or more of the PAPs 16 a, 16 b and 16 c and to acontrol module 30, over respective paths 26 a, 26 b, 26 c and 26 d(generally 26). In various embodiments, the communication medium 24 is aphysical structure such as a back plane. In other embodiments, thecommunication medium is the same medium that is used by the energy beams18. In one example, the communication medium is air (e.g. a terrestrialenvironment). In another example, the communication medium is at least apartial vacuum as found in orbital altitudes or outer space. In anotherexample, the communication medium is either fresh or salt water.

Communication between the devices 14 and the PAPs 16 is used to optimize(e.g. maximize) the transfer of power from the PAPs 16 to the devices14. For example, each of the beams 18 are directed (e.g. steered)towards one or more devices to maximize a received energy level at therespective device as communicated from the respective device to at leastone of the PAPs 16. Similarly, the phase for each of the energy beams 18is adjusted by the PAPs 16 to maximize the received energy level at therespective device. In some embodiments, the polarity of each of theenergy beams 18 is also aligned to maximize the received energy at therespective device. Communication over the paths 26 and 28 and throughthe medium 24 includes for example, the use of one or more of the IEEE802.3 Ethernet standards, one or more the IEEE 802.11 WiFi® standards,one or more of the Bluetooth® standards, one or more of the IEEE802.15.4 ZigBee® standards, a proprietary communication protocol, anywired or wireless communication protocol or any combination of theforegoing.

FIG. 2 shows a functional block diagram of the control module 30 ofFIG. 1. The Control Module 30 includes a Phasor Decomposition Module 32,a Switched Beam Polarization Alignment Module 34, and a ReceiverLocation Determination Module 36. In one embodiment, each module of theControl Module 30 is implemented with circuitry. Various embodiments ofthe Control Module 30 include one or more of the Phasor DecompositionModule 32, the Switched Beam Polarization Alignment Module 34, and theReceiver Location Determination Module 36 to implement the respectivefunctions described herein.

Phasor Decomposition Method (PDM):

A Phasor Decomposition Method (PDM) described herein reduces the numberof phase adjustments typified by iterative methods (e.g., GradientAscent). Improvements in the time required to achieve optimum powerdelivered to an energizable device (e.g., sensor, tag or battery) is onthe order of 1,000 to 10,000 times for 10 to 100 sensor tags per PAPrespectively when compared to iterative methods. Very fast transmission(e.g., less than 100 us) of information containing Phasor contributionsfrom each PAP received at each energizable device location is sent fromthe energizable device to either one or more PAPs, or other devices thatcontrol the PAPs. The speed of the transmission is limited by thecommunication bandwidth between PAPs and the energizable devices and thenumber of available communication channels (e.g., in the time,frequency, or spatial domains). This Phasor information can also be usedfor dynamic localization of sensor tags or to detect motion of people inthe way of the communication path between a PAP and an energizabledevice. Dynamic localization is particularly beneficial in changingenvironments (e.g. people walking or sensors moving), a busy warehouse,industrial settings (e.g. with conveyor belts), coffee shops, stores,houses or an office and can be used to help compliance with emissionstandards.

With PDM, the time required to achieve optimal power (Topt) at allsensor tag locations is Topt=4*N*Ts+Tcomm, where N is the number ofPAPs, Ts is the phase/polarization update rate (e.g., 2 us to 50 us),and Tcomm is a communication channel update rate (e.g., 1 ms-100 ms). Incontrast, iterative methods, such as Gradient Ascent (e.g., HillClimbing) require multiple iterations to find the maxima leading to Topton the order of 20*H*(N+1)*(Ts+Tcomm) to 100*H*(N+1)·(Ts+Tcomm), where His a number of sensors per TX and the factors of 20 and 100 are thenumber of iterations required in order to reach optimum. Additionallythere is no guarantee that an optimal power derived by a Gradient Ascentmethod will not be a local optimum.

PDM is a method for obtaining the amplitudes, phases and polarizationvector phases of a phasor of an EM wave transmitted from eachcontributing PAP for each energizable device without delays due toiteration, (limited by the number of simultaneous communicationchannels). The radio frequency (RF) power signal at each sensor taglocation is a combination of line-of-sight, reflections, and diffractionof multiple waves from multiple PAP sources in addition to noise.

The description of PDM uses general assumptions and terms as follows. APower Access Point (PAP) is at a location where RF energy is radiatedfrom. An energizable device is a device that receives radiated RF energy(e.g., an RFID sensor tag). An energizable device is also referred to asa Receiver of Applied Power (RAP). For the purposes of PDM calculation,the phase accuracy (e.g., due to drift) of each PAP with respect to eachother is assumed to be small (e.g., <30°) during the phase adjustmentperiod, which, in practice, is in the range of Ims to 100 ms, but couldbe as small as a few micro-seconds and as large as many seconds,depending on the type of synchronization used and the resultant phaseaccuracy.

The term “phase” refers to the phase of a 2D Phasor, or “Phasor”. Theterm “Phasor” refers to a two dimensional (2D) Phasor represented byeither a complex number or a pair of vector coordinates in polarcoordinate system, as used throughout this disclosure. Generally, thePhasor can be represented in any other coordinate system. The term “3DPhasor” refers to a three dimensional (3D) vector formed by summing two2D Phasors at each orthogonal EM wave polarizations. Since EMpolarization is generally a “polarization vector”, an EM wave can bedecomposed into two constituent orthogonal polarizations (e.g.,vertical/horizontal), each one having an independent 2D Phasor (e.g.,amplitude and phase). The amplitudes in this case would be theamplitudes of the polarization vector, (e.g., same amplitudes as of theconstituent 2D Phasors), while the phase of the polarization-vector isthe (extra) 3rd dimension of the 3D Phasor “polarization angle” (e.g., a90 degree polarization angle corresponds to Circular Polarization).

An RSSI reading is a reading of an average power, averaged for at leastfew cycles of the fundamental (center, or carrier) frequency, such as915 MHz. Due to the narrow bandwidth occupied during phase adjustmentsit is assumed that the propagation channel from any PAP to anyenergizable device can be modeled as a complex constant, and theresultant Phasor at the energizable device location is multiplied by acomplex constant for each PAP, resulting in a summation of a product ofchannel constant per PAP by a PAP's Phasor.

Regarding Fade mitigation, if significant fading is expected then aphase shifting update rate can be reduced to reduce the occupiedbandwidth to a point where fading loss is below a threshold. The centerfrequency can also be adjusted in addition to increasing the phaseadjustment period. Either of these two approaches can be done with afeedback from an energizable device. For example, if an energizabledevice is positioned in the place where waves from one or multiple PAPsadd destructively (independent of the 3D phasor), then the centerfrequency can be adjusted, until either the energizable device startsresponding, or the reported RSSI is improved.

Unlike Hill Climbing, PDM in its simplest form, involves adjustingphases by 90° and 180° from some initial phase (Ø0) for eachcontributing Phasor, except last one. The 90°/180° phase shifts arechosen primarily for easing the computation, and also to achieve abigger degree of independence of equations (e.g. orthogonality) due toquantization, and other noise, which otherwise would be stronger forsmall angular changes.

With PDM, a Phasor sum can be represented in terms of a single Phasorand the sum of the rest of the Phasors. The phase of that one Phasor isadjusted by 90, 180 degrees creating 3 equations (0°, +90°, +180°) and 3unknowns, from which the phase and amplitude of that single Phasor iscalculated. Although the phase solved is the phase between a singlePhasor and the sum of the rest of the Phasors, and not the total sumPhasor, (which is constant). An additional computational step is thenperformed to convert it to a phase relative to the total sum of thePhasors. This procedure is repeated N−1 times to get amplitudes andphases of all individual Phasor components (the last Phasor is trivialas the sum is known and the rest of the Phasors are known). Theresultant combination of Phasors with amplitudes and phases can thenoptimized in “one shot” by adjusting all phases simultaneously to anoptimal configuration. This procedure has an added advantage to get allphases and amplitudes at ALL sensor locations all at once (as long asthey receive enough power, and factoring in time multiplexing nature ofcommunication channel).

At a particular time interval, PDM adjusts phases of a signal comingfrom each PAP sequentially. For each PAP the phase is adjusted by 0°,+90°, +180° at each of two polarization directions, (e.g., a total of 6phase/polarization values), or any other 6 angles with sufficientdifference (other angles that can be decomposed to 0°, 90° angles),while the phases/polarizations of the rest of the PAPs remain at 0° andwith a fixed (predefined) polarization. The procedure is repeated foreach PAP in a cluster (or a subset). In some embodiments, time slots forphase changes are assigned for each PAP, based on their proximity toeach other and to energizable devices to improve the time interval ofnear-optimal Phasor combinations.

The resultant RSSI readings at each energizable device corresponding tophase/polarization changes at each PAP are recorded by the energizabledevice when it detects certain jumps in RSSI. This vector of RSSIreadings corresponding to 0°, +90°, +18° phase changes at each of 2polarizations for all PAPs is sent to PAP(s) and it correlates RSSIchanges to phase changes. In another embodiment, RSSI measurements arestarted based on synchronization between PAPs either by synchronizing tothe Master or predicting the PAP phase adjustment time based on otherinformation (e.g., communication from PAPs; spurious emissions duringphase jumps).

After receiving the RSSI vectors from all sensors, PAPs then solve theequations necessary to get the Phasor of each contributing PAP(including itself and other nearby PAPs). It is also possible for thesensor tag to determine the time slot boundaries (e.g., by observingRSSI changes or the SYNC signal) and/or to solve the equations andreturn the answer to reduce the size of payload it sends (faster, lessenergy consumed), or it can wait for a sync packet from Master PAP andtime the exact moment when phases are expected to change.

FIG. 3 illustrates, an example embodiment of a PDM for adjusting phasesof three PAPs including signaling between a Master PAP, a Slave 1 PAP, aSlave 2 PAP and a plurality of energizable devices (e.g., sensors tags).Specifically, the flow events with synchronization (Sync), RSSI readingsand phase adjustments are shown. A total of six PAP phase adjustmentsare made, including 0 degrees, 90 degrees, and 180 degrees for each oftwo polarizations, (e.g., a total of six adjustments).

In various embodiments, the PDM of FIG. 3 is performed for twice, foreach of two phasor polarizations. In embodiments, where polarizationalignment is not required, only one PDM cycle is performed. For eachpolarization, the PDM cycle begins with a synchronization (Sync) pulse50 transmitted by the Master PAP, and received as a Sync pulse 52 and 54received by a first energizable device (Slave 1) and a secondenergizable device (Slave 2) respectively. A polarity is chosen for thetransmission from the Master, Slave 1 and Slave 2. At 56, 58 and 60, theMaster PAP sequentially adjusts the phasor for the Master, Slave 1 andSlave 2 respectively, based on a phasor decomposition calculation from aprevious PDM cycle. At 62, 64, and 66, the Master PAP transmits a phasorwith a phase adjustment of 0 degrees, 90 degrees and 180 degreesrespectively, while the phase adjustment of the Slave 1 PAP, and theSlave 2 PAP remains at 0 degrees. An RSSI level is measured at eachenergizable device for each of the three transmitted phases by theMaster PAP. At 68, the RSSI values determined from each energizabledevice, corresponding to each phase of time slots 62, 64 and 66 for eachPAP (e.g., Master, Slave 1 and Slave 2) are transmitted to a device forperforming a subsequent phasor decomposition calculation. In oneembodiment, the device receiving the plurality of RSSI values is theMaster PAP.

At 72, 74, and 76, the Slave 1 PAP transmits a phasor with a phaseadjustment of 0 degrees, 90 degrees and 180 degrees respectively, whilethe phase adjustment of the Master PAP, and the Slave 2 PAP remains at 0degrees. An RSSI level is measured at each energizable device for eachof the three transmitted phases by the Slave 1 PAP. At 78, the RSSIvalues determined from each energizable device, corresponding to eachphase of time slots 72, 74 and 76 for each PAP (e.g., Master, Slave 1and Slave 2) are transmitted to a device for performing a subsequentphasor decomposition calculation. In one embodiment, the devicereceiving the plurality of RSSI values is the Master PAP.

At 82, 84, and 86, the Slave 2 PAP transmits a phasor with a phaseadjustment of 0 degrees, 90 degrees and 180 degrees respectively, whilethe phase adjustment of the Master PAP, and the Slave 1 PAP remains at 0degrees. An RSSI level is measured at each energizable device for eachof the three transmitted phases by the Slave 2 PAP. At 88, the RSSIvalues determined from each energizable device, corresponding to eachphase of time slots 82, 84 and 86 for each PAP (e.g., Master, Slave 1and Slave 2) are transmitted to a device for performing a subsequentphasor decomposition calculation. In one embodiment, the devicereceiving the plurality of RSSI values is the Master PAP. Subsequently,the PDM cycle repeats for the second polarization for embodiments wherepolarization alignment is required.

FIG. 4 is a flowchart representation of pseudo-code for phasordecomposition. The polarization alignment calculation begins with thefollowing three equations representing a phasor with zero phaseadjustment, with 90 degrees of adjustment, and with 180 degrees ofadjustment, respectively:

S ² _(1N0) =A ² ₁ +S ² _(2N)+2*A ₁ *S _(2N) cos(Ø_(o))  [1]

S ² _(1N90) =A ² ₁ +S ² _(2N)+2*A ₁ *S _(2N) cos(Ø_(o)+90°)  [2]

S ² _(1N180) =A ² ₁ +S ² _(2N)+2*A ₁ *S _(2N) cos(Ø_(o)+180°  [3]

By rearranging equations [1], [2], and [3] we derive the followingequations [4] and [5], from the phase angle Ø_(o) and amplitude A₁ aredetermined:

tan(Ø_(o))=2*[ΔS ² ₉₀ /ΔS ² ₁₈₀]−1  [4]

β₀=[sin(Ø_(o))*A ₁ /S _(1N)]  [5]

In the equations [1], [2], [3], [4] and [5], S_(2N) represents the sumof all phasors except phasor 1; S_(1N0), S_(1N90), and S_(1N180)represent the total sum of phasors, when phasor 1 is in the initialstate (zero phase adjustment), when phasor 1 is rotated by 90 degrees,and when phasor 1 is rotated by 180 degrees, respectively; Ø representsthe phase angle between phasor 1 and S_(2N); and β₀ represents the phaseangle between phasor 1 and the total sum of phasors S_(1N). Afterdetermining the phase angle and the amplitudes with equations [4] and[5], the procedure is repeated for another phasor, except the last one,which can be computed from the previous phasors. In total, there are1+2*(N−1) RSSI measurements and phase adjustments.

PAP Synchronization and Master Selection Methods:

In one embodiment, a single master PAP is chosen. In another embodiment,there are no master PAPs, rather collaboration occurs between the PAPsto perform frequency tuning.

In one embodiment with comm-channel based synchronization using a SYNC,time-stamped message, the best master is the one that can communicate aSync message to all PAPs with a low probability of error, (e.g., highestcommunication channel Signal to Noise Ratio (SNR) or lowestinterference). In one embodiment using a separate RF frequency forsynchronizing PAPs, the highest SNR on Sync RF frequency is required.

Example embodiments for synchronization between PAPs include one or moreof the following: A wireless embodiment, includes an optical (e.g.,Infrared) communications channel between the PAP and the energizabledevice, using one of a 100/120 Hz harmonic of a fluorescent light(passive), and sending pulses or a modulated signal from a master. Awireless embodiment, includes an acoustic communications channel betweenthe PAP and the energizable device, wherein the master sends a tone ormodulated signal, or uses an external source of a known signal (e.g.,120 Hz humming). A wireless embodiment, includes a radio frequency (RF)communications channel between the PAP and the energizable device,wherein the master PAP sends a continuous wave (CW) wave or modulatedsignal that other PAPs synchronize to.

An embodiment includes a distributed system wherein every PAP exchangestiming packets or (CW bursts) with every other PAP and adjusts theirrespective clocks to the average, which eventually converges. Anexternal source of a known signal is used by the master PAP, including a100/120 Hz or a harmonic of fluorescent lights or transformers, a Wi-Fi(timing) signal from router(s), a cellphone signal, or timing signalfrom a cellphone tower, or a GPS/Glonass, (with no master, but with anexternal antenna at each PAP.

In one embodiment of a PDM system, radioactive emission is used forsynchronization, including an external source (e.g., smoke detectors),or an open loop isotope timing device (e.g., a Caesium atomic clock). Inone embodiment of a wired system uses existing AC power lines forsynchronization by locking to the 50/60 Hz or a harmonic thereof. Inanother embodiment, a master sends a Sync packet over a power line. Inanother embodiment having a distributed system of PAPs, every PAPexchanges timing packets (e.g., using Ethernet over a power line, orwith load modulation). In another embodiment of a wired system, one ormore PAPs use USB, RS232, or Ethernet. In another embodiment of a wiredsystem, one or more PAPs use a dedicated coax with a single tone ormodulated signal, or similar single wire. In another embodiment of awired system, one or more PAPs use a guided wave propagation (e.g., asurface wave in drywall or in air ducts).

Synchronization of PAPs with a Master:

The deployment is assumed to be known (e.g. IP network topology, PAPclusterization) and masters are either assigned manually, or by analgorithm. In the case of Wi-Fi and similar protocols, there is anetwork discovery stage of operation, (e.g., at startup and once every Xseconds), to get the MAC and/or IP addresses of PAPs connected withinthe cluster. In various embodiments, a known list of possible MACaddresses for a particular deployment is programmed into each PAP. Inother embodiments, there is also Telnet/SSH to the router, getting anARP table and looking for MAC addresses ranges corresponding to PAPs,with appropriate attention to security issues. After a list of connectedPAP MAC and/or IP addresses is known, PAPs communicate with each other,(every Y seconds in one example).

There are many different types of information exchanged, such as Wi-Fibased coarse SYNC, PAP_MASTER_RSSI table, RAP_table (short/longversion), sync messages, user messages (user to/from RAP sensor),status, and configuration for example.

If a master is not selected manually, during startup, or when a new PAPis discovered on the PAP cluster network, a master selection algorithmis initiated, (optionally suspending other tasks). In one exampletechnique for master selection, all PAPs in the cluster are tried to bemaster, one by one, (by using a MAC address sort, or IP addr sort forexample). For each candidate PAP, the communication (e.g., comm) channelof the candidate is set to TX, while other PAPs are set to RX. Anymessage is broadcast by the candidate via a comm channel, (ideally syncmessage, to reduce sync time), and RSSIs of this message are measured byall non-candidate PAPs, (at a predefined interval starting from Wi-Fibased coarse Sync, which is well within latency fluctuation of therouter, such as 1 second). The PAP_MASTER_RSSI table is filled out byeach PAP in the cluster (candidate ID, RSSI from candidate) for eachcandidate. At the end of the master trials each PAP has a table of RSSIfor each possible master. These tables are exchanged by PAPs throughWi-Fi network or other comm channel. Since each PAP has the same set oftables, (same) decision is made on who should be the master. Since thebest master is assumed to be the one which provides lowest probabilityof error SYNC message to all other PAPs in the cluster, a maximizationof minimum RSSI in PAP_MASTER_RSSI table is one such choice, whileanother choice could be maximization of a weighted goal function such asScore=TotalRSSI*W1+minRSSI*W2, if minRSSI>threshold, Score=minRSSI*W3,if minRSSI<threshold. Clusterization is also optionally done at thispoint, and master per cluster is selected based on comm-channelconnectivity graph and minRSSI values: masters are added until minRSSIis above threshold. For example, if we have a warehouse with 20 PAPs,and had one master in the middle it would cover 15 of PAPs but ones onthe edges may not be receiving the Sync signal. To rectify this, weincrease the number of masters, and try to optimize minRSSI again, untilminRSSI is over the threshold value.

All PAP_MASTER_RSSI tables, side by side, for selecting one master (onlya triangular portion of the table is unique, without the diagonal):

PAP_1 PAP_2 PAP_N Total Candi- Candi- . . . Candi- min date ID RSSI dateID RSSI . . . date ID RSSI RSSI 1 N/A 1 A2 . . . 1 AN min(A1 . . . AN) .. . . . . . . . . . . . . . . . . . . . . . . N Z1 N Z2 . . . N N/Amin(Z1 . . . ZN)

After a master is selected for the first time, the master sends a syncsignal, and other PAPs synchronize their clocks. Consecutive syncmessages are sent by master at predefined accurate interval, such as 1 sto 5 s, (for a 1 ppb/s XTAL), derived from master's high stabilityOvenized Crystal Oscillator (OCXO) (e.g., <1 ppb/s & 10 ppb/day driftOCXO is used in one prototype). Other PAP nodes compute the differencein time, which should be the time of sync—interval relative to their ownOCXOs and compare the difference (highly deterministic chain, highpriority interrupt on sync packet RX, MCU based counter based on OCXOclock). After the PAPs compute the difference in times, they calculatethe relative frequency shift of their OCXO compared to master's andadjust OCXO tuning (according to a lookup table)+feedback+driftestimation. Due to the fact that the PDM algorithm is very fast (e.g.,10 us-1 ms) per PAP, even with OCXO drift the phase during that 10 us to1 ms will not change significantly. At, for example, an unadjusted <1ppb/s drift, the phase changes about <3 deg in 8*1 ms (8 PAPs). Butduring the time with no phase transitions (phases for optimal powerdelivery), 10 ms to is, the phase will shift by an amount, which dependson sync interval, and optimal power interval. This can be reduced bychanging sync and optimum power interval adaptively (e.g., 1 second syncperiod Ts, 100 ms optimum power period Topt: <18 deg max error, muchless on average).

Synchronization of PAPs without aMaster:

Similar to the master selection procedure, in one example technique eachPAP is tried to be a master, and PAP_MASTER_RSSI table is filled out byeach PAP, but not in the cluster as before, but based on all PAPs indeployment. Unlike single master per cluster method, in this case, themaster trial procedure is done every 100 ms 2 s (not just at startup orwhen a new PAP is added). Along with Master candidate ID, RSSI fromcandidate, OCXO (Ovenized Crystal Oscillator) frequency difference iscalculated for each candidate. An average of OCXO frequency differencesis calculated and applied. This is repeated for each PAP. Over time allOCXOs will reach global average, same frequency. For example, twoseparate clusters of PAPs with one PAP added in between at a laterstage, the average of each cluster is independent and settled, butadding a PAP in the middle will set an initial value of the middle PAPto the average of two clusters, while putting a small pressure on bothclusters that moves their average, slowly, towards the middle PAP, andeventually the system will equalize. This procedure is much slower thanthe one with a single master, but can be sped up significantly if PAPsform a deterministic low-drift mesh network, avoiding comm-channel-basedclusterization, and syncing to an overall average in Nsync intervals,where N is a mesh network depth, or max number of hops. The time toreach Sync is N times greater with a mesh network and perhaps hundredsof times greater if not using a mesh network (due to ‘rolling’ average),compared to master per cluster approach.

Energizable Device Synchronization to PAP Master:

One embodiment includes listening to the same SYNC signal as being sentfrom Master PAP to slave PAPs (as done in the present prototype).Another embodiment includes performing multiple RSSI readings anddetecting changes in RSSI that correlate to the phase/polarizationchanges performed by PAPs.

PDM Prototype Implementation:

The PAP sync is done over a comm-channel, which the energizable devicecan listen on. When an energizable device has enough energy to listenfor the duration of PAP sync cycle, the energizable device changescomm-channel freq to PAP sync channel and waits for sync. Afterreceiving sync the energizable device goes to sleep, (with a timer on),and next wakes up on just before expected phase change if it has enoughenergy to perform transmisstion of the RSSI vector, (+ADC readings), ifnot then the energizable device sleeps some more (+Tsync err). If abrownout happens the procedure is repeated when there is again enoughenergy. Initial charging is done with a random phase, so it might take awhile (statistically) to gather enough energy for first sync RX andfirst RSSI TX.

If the energizable device cannot receive sync, but has enough storedenergy, it will look for RSSI changes and its variance over time anddecide where the phase adjustment window is statistically (assuming thatoptimal power duration is constant). During optimal power interval thephase will change, (but slower), and will be proportional to referencedrift+multi-RAP optimal power delivery phase adjustment; the phase cannot jump quickly to change optimal combination for each energizabledevice. To detect changes in RSSI during phase changes the energizabledevice has to sample with ADC at higher rate than phase changes. So, forexample, if 10 us phase changes at PAP are used RAP ADC has to sampleat >300 KHz, but only during phase change interval=N*5*10 us+variance,where N=number of PAP, and variance is error due to desync.

If the energizable device receives some low energy due to a randomphase, and charges at some point, but is below a harvester threshold fora long duration, the capacitor will discharge, and the energizabledevice will not have a chance to respond. In this case the solution doesnot improve the range, but this is a very rare case statistically.

Comparison to Iterative Algorithms:

Iterative algorithms take multiple reading of the RSSI values duringoptimization. Common types of algorithms include Gradient Ascent (HillClimbing), Genetic Algorithm, Min/Max, LMS, and variations/combinationsof these with added randomization to avoid local optimum.

Disadvantages of Iterative methods include multiple communicationinstances to achieve optimization. Since the RSSI needs to be measuredat multiple points, there needs to be constant communication between RXand TX. Disadvantages of Gradient based methods include amplified noise(e.g., less robust in a realistic scenario). Gradient calculation isessentially a derivative calculation and small changes in independentvariable lead to small changes in the dependent variable, (e.g., smallphase changes greater than small RSSI changes). Disadvantages ofRandomized and Genetic Algorithm based methods are that noise is notamplified at the beginning, but will be near the optimum. Additionally,convergence takes much longer, but convergence will occur at an absoluteoptimum point, but on the order of 10 to 100 times lower than with HillClimbing.

Advantages of Iterative methods include not disturbing RSSI far from theoptimum, after the optimum is achieved. Iterative methods also use asimple computation, where differences are computed for RSSI and thephase is adjusted by multiplying a constant, (e.g., gain constant), bythe derivative, (e.g., partial derivative with respect to particularTX). The iterative method is a bit more computational complex comparedto the Genetic Algorithm.

An embodiment of a Phasor Decomposition Method (PDM) finds allconstituent signal amplitudes and phases at an energizable device. Thetotal amplitude is measured 2*(N−1) times by adjusting individual Phasorphases by 90°, and 180° all sequentially (−2*(N−1)*50 μs+Tcom), where Nis the number of corresponding Phasors. PDM solves for all phases andamplitudes at all energizable device locations all at once (limited bythe comm. channels), and thus optimizes power at all locations at oncegiven power allocation priority. Compared to Hill Climbing, the speedimprovement of PDM is on the order of 20*N-100*N, where N is number ofPAPs, (and the factor 20-100 depends on number of steps in Hill Climbingalgorithm).

Consider a case with N PAPs with the same frequency and adjustablephases. At the receiver these amplitudes and phases are arbitraryaltered due to multi-path propagation. For the purpose of thisdisclosure, the phases and amplitudes do not change in time, (e.g.,measurements are done much faster than changes in amplitude/phase). Toalign the phases of the incoming waves at the receiver, a variety ofmethods can be employed, depending on trade-off of response speed,immunity to changes/noise. Phases can be adjusted incrementally, toslowly attempt to reach some optimal (typically local maximum) point.This can be done with a variety of algorithms, such as GradientAscent/Hill climbing, or Genetic Algorithms, or one can estimate thepresent state of phases/phases of individual Phasors using PDM to reacha global maximum in one step after having phases/phases. Due to thefeedback nature of Hill Climbing, there needs to be constantcommunication between RX and TX for each “step climbed”, which is notthe case with PDM, as it can provides optimal in “one shot” bycorrelating phase changes and RSSI changes, thus saving power used forcommunication.

The effectivity of wireless RF power transmission is limited byincreases in the operating frequency as well as an increased physicalseparation between PAPs and energizable devices, (e.g., user devices,receivers, or tags). These limitations are overcome by the use ofmultiple PAPs. The random deployment of multiple PAPs will not result inoptimal reception at the location of the energizable device due tohaving multiple incoming waves with unknown, non-cohered phases, allconstructively or destructively interfering with each other.

Further inefficiencies result from the polarization from each individualPAP directed towards an energizable device and the resulting summationwave at the location of the energizable device, specifically from thepolarization of each PAP not being the same at the receiving location(e.g., due to reflections from the transmission medium). Polarization isalso unknown and non-cohered at each energizable device and the effectof having arbitrary locations for each PAP, each with unique reflectionsand other conditions, will further complicate alignment of polaritiesarriving at the use device from a plurality of PAPs.

Even though a PAP may transmit a linearly polarized wave, thepolarization received at an energizable device may be any combination oforthogonal polarizations due to multipath effects. The resultingpolarization may be rotated linear (as discussed above), right orleft-handed circular, or slant elliptical polarization.

In various embodiments, similar algorithms used for phase alignment areused to ensure that the polarization of the resulting summation wave atthe receiving device has the same polarity as the constituent waves fromeach PAP. In one example the polarity is vertical. In other examples,the polarity is one of vertical, slant, horizontal, circular, ellipticalor slant elliptical. For clarity in the exposition, in the followingexample embodiments, the aligned polarity is vertical. It should beunderstood that in other embodiments, other polarities are realizablewithout departing from the scope and spirit of this disclosure.

A switched beam is used to steer the transmit beam from each PAP. Aswitched beam structure is used requiring only a Butler matrix,incorporating cross-over structures, and a single-pole-multi-throw(SPMT) switch. In some embodiments, the crossover structure is a “WightCrossover” structure. An example embodiment of this structure is shownin FIG. 6 for a four-element array. In other embodiments, a differentnumber of elements are used (e.g., eight or sixteen elements). The fouroutputs from the SPMT switch each provide a different set of phaseshifts to the four signals reaching the four patch antennae. Thesedifferent sets of phase shifts cause the composite beam to form itsmaximum in a different direction or spatial angle (similar to a phasearray). This corporate feed will provide a power boost of M at theenergizable device, where M is the number of elements compared to asingle antenna element.

Only energizable receivers that are at the intersection of the multiplebeams from the multiple transmitters will be illuminated or energized.Within that intersection space, the multiple beams will have differentpolarizations at the different locations of the multiple receivers dueto multipath propagation. The correct selection of the multipletransmitter polarizations are chosen such that either a) each receiveris sequentially receiving all transmitted signals with the samepolarization, or b) all receivers are simultaneously receiving alltransmitted signals with the largest “minimum-received-power” achievableat one of the receivers. This largest minimum-received-power occurs atany one of the receivers, wherein the other receivers receive more thanthe minimum-received-power. In various embodiments, the polarizations atthe multiple transmitters are iteratively adjusted following a method(e.g., hill climbing or PDM), until the largest minimum-received-powerat one of the receivers is achieved.

According to various embodiments, multiple PAPs are used to offsetenergy losses in the RF energy beam received at the receiving device,due to an increased separation distance between the PAPs and theenergizable device. The energy beams received at the energizable deviceby their respective PAPs described herein, are all phase cohered byphase locking techniques ensuring all incoming signals at theenergizable device arrive in phase, regardless of the position of eachindividual PAP.

According to the various embodiments, both the received phase and thefrequency of each PAP used to simultaneously send power to one or moreenergizable devices are fixed and identical to the respective phase andfrequency of all other PAPs. In one embodiment, the aforementioned,fixed and identical phase and frequency is achieved by phase locking allPAPs within range of a master PAP to a single predetermined master clockfrequency.

The respective phase and frequency at the PAPs is locked continuously,while being monitored and adjusted in real-time. However, at thelocation of the energizable device the incoming polarization receivedfrom the multiple PAPs will not be the same because the PAPs are not allat the same physical location, nor is the path between each PAP and thereceiving device the same. Each PAP has a unique source of reflectionsand other operation conditions relative to other PAPs.

The respective incoming EM waves of energy beams from multiple PAPs,(also referred to herein as “transmitter” or “Tx”) may each have adifferent polarization at the location of the energizable device, (alsoreferred to herein as “Rx”), as the PAPs are not physically aligned inspace. In a worst-case example, the polarization of each EM wave at theRx location will be orthogonal to another EM wave, (e.g., vertical andhorizontal, or right-hand circular and left hand circular). In this casethe total received power at the receiving device will be reduced bypolarization misalignment.

In many embodiments, the multiple PAPs and receiving devices are allnominally within a horizontal plane, (e.g., on the same floor of abuilding), and their resulting directions of propagation (e.g., Poyntingvectors) of all transmitted EM waves are nearly in the horizontal plane,making it possible to align all the incoming wave's polarization.

In one embodiment, the respective improvement in power received at thereceiving devices, produced by polarization rotation of linearpolarization from each Tx, results in all incoming waves at the Rxlocation to be vertically co-polarized, thereby increasing the Rx powerby a factor of N, where N is the number of PAPs.

Use of the aforementioned technique for achieving polarization alignmentresults in an N*N*N=N³ improvement in the power received at thereceiving device, compared to using a single PAP. This improvement isdue to three factors: a) use of N multiple PAPs, b) phase alignment ofEM waves at the receiving device, and c) polarization alignment of EMwaves at the receiving device. In comparison, arbitrarily deployed PAPswithout phase and polarization alignment obtain only an N improvementover using a single PAP.

The polarization rotation used here, is achieved using polarizationtechniques on the antennas at the PAPs. In a first example, dualorthogonal polarizations are simultaneously transmitted, each having aspecific amplitude, normalized between −1 and 1, from each PAP as shownin FIG. 5. The respective maximum polarization rotation needed for eachPAP is +/−90 degrees to achieve vertical polarization summation at thereceiving device.

With reference to FIG. 5, in the embodiment 130, a single feed 140 isamplified with a first variable gain amplifier (VGA) 134 and combined ata patch 132 with a second feed of the same signal. The second feed isamplified with a second VGA 136 and phase shifted with a phase shifter138 over a range of zero degrees to 360 degrees. In one embodiment, thephase shifter of the second feed nominally shifts the phase of thesignal by plus or minus 90 degrees. In another embodiment, both thefirst feed and the second feed are phase shifted to produce adifferential phase shift between the first feed and the second feed fromzero degrees to 360 degrees.

Furthermore, in one embodiment having three or more PAPs, the individualreceived polarizations at the location of the receiving device need tobe vertical to enable full polarization alignment. Alternatively anotherpolarization is used, being the same for each EM wave arriving at thereceiving device from a respective PAP.

For the aforementioned PAPs, all transmitting a linearly polarized wave,the received polarization at the energizable device will be acombination of orthogonal polarizations due to multipath. This willresult in polarizations which are rotated linear, right and left-handedmultiple polarizations or slant elliptical polarization of the waves atthe energizable devices.

According to some embodiments, the multiple PAPs individually adjusteach of their polarizations of the EM waves as received by theenergizable devices to form a resulting vertical wave at the receivingdevice.

The respective multiple PAPs simultaneously transmit dual orthogonalpolarizations, each orthogonal polarization having a specific complex(amplitude and phase) normalized between 0 and 1. As is shown in FIG. 5,each transmitter has two amplifiers with variable gain (VGA) and atleast one of them includes phase shifting capability between zero and360 degrees.

In some examples, the multiple PAPs will use predetermined thresholdvalues to make decisions on whether polarization alignment is needed.Furthermore, in various embodiments, the polarization alignmentprocedure uses measurements from the Receive Strength Signal Indicator(RSSI) from each energizable device. In other embodiments, other methodsof measuring received power at the energizable device are used.

The RSSI measurement from each energizable device is transmitted back tothe PAPs currently being aligned and, in one example, a hill-climbingalgorithm is used to guide the polarization of each access point to itsfinal state. In another embodiment, a PDM method is used to guide thepolarization alignment to its final state.

In some embodiments, the respective PAP, uses switched beambeam-steering rather than phase array beam-steering. Phase arrayapproaches perform exceedingly fast beam-steering, not required forpower applications. Furthermore, phase array systems also require atleast one phase shifter for each antenna element increasing systemcomplexity and cost. The switched beam-steering structure 150 is shownin FIG. 6 and requires only one Butler matrix 160 (utilizing four hybridcouplers 162, 164, 168 and 170, and two Wight Crossover structures 166,and 172), and one single-pole-multi-throw switch 174. The embodiment 150of the switched beam-steering structure includes four instances ofcontrollable slant linear polarizers 152, 154, 156 and 158.

The switched beam beam-steering system incorporates a master phaseshifter 176 to carry out the previously described phase alignmentbetween multiple PAPs. A resulting power boost of M is achieved by usingthe switched beam antenna array approach. Here M represents the numberof antenna elements compared to a single element, and is an additionalfactor to the previously described N*N*N increase.

In applications involving a multitude of receivers, such as inwarehouses where the energizable devices are Radio FrequencyIdentification (RFID) tags, the determination of the location of eachtag is important. Not only is it necessary to energize and read the RFIDtags, it is desirable to determine on which shelf the tag is located.Since a warehouse is large and contains many stationary metal objects,(e.g. shelves), and dynamic metal objects, (e.g. forklifts), standardlocation techniques based on Direction Finding (DF), Angle Of Arrival(AOA), Time Difference Of Arrival (TDOA), and relative received powerlevels are not useful. There is a need therefore for locationtechniques, which work in a highly multipath environment.

In various embodiments, a power transmission system delivers power toreceiving devices such as RFID tags from a group of PAPs, each of whichis coherently locked to a common frequency. By adjusting the relativephase of the transmitted signal from each PAP, energy “bubbles” arecreated in three-dimensional space, and power is delivered to allenergizable devices in each “bubble”. As the energy “bubbles” are movedthrough the three dimensional (3D) space by changing the relative phasesat the Power Access Points, different sets of energizable devices areenergized. It should be noted that due to the multipath environment,which exists in the 3D space (e.g. warehouse), the actual locations ofthe “bubbles” may not be unambiguously determinable a priori.

It is thus desirable to determine the location of the energy “bubbles”for each set of relative phases at the Power Access Points, and also toreduce the number of “bubbles” simultaneous formed in the 3D space toone.

It should be noted that because an energy “bubble” is created from thephase alignment of the transmitted signals from each PAP, its size isrelated to the wavelength of the transmitted signals; nominally a halfwavelength in each direction. For a transmitted signal at 915 MHz, thesize of the bubble will be approximately 16 cm×16 cm×16 cm.

Location Determination:

In embodiments that include a warehouse, each energy “bubble” willilluminate a group of energizable devices (e.g., RFID tags), whereineach device is in close proximity to other device. As the energizabledevices report their identity, (and data), the identities can begrouped. As the energy “bubble” is moved to an adjacent but undeterminedlocation, some of the energizable devices will continue to report back,(because they are still being energized by the energy “bubble” in itsnew position) while other receiving devices (tags) will not (e.g., theyare no longer being energized by the “bubble”). After a scan of thethree-dimensional space by the “bubbles” a connectivity map can becreated to show the nearest neighbors for each energizable device.

This connectivity map does not provide a physical location of eachdevice. However, several “reference” energizable devices (e.g. RFIDtags) can be placed throughout the three dimensional space in knownlocations. Accordingly, the energizable devices are located as nearestneighbors to the reference tags, and are located by using interpolationbetween groups associated with different reference tags based on theconnectivity map to determine the position of all of the energizabledevices. In some embodiments, such as those in which closeness of areceiving device to a PAP is determined, the respective locations of thePAPs are also used as reference locations. Collectively, the locationsof the reference energizable devices and the locations of the PAPs areall reference locations.

In various embodiments, multiple energy “bubbles” will exist for eachset of PAP relative phase settings, and the connectivity map will createmultiple ambiguous locations for the energizable device locations.Advantageously, the number of energy “bubbles” simultaneously createdwill diminish as the number of PAPs employed to create the energy“bubbles” is increased.

First Method of Location Ambiguity Resolution:

The location ambiguity difficulty can be removed with the creation of asingle energy “bubble” rather than the multiple “bubbles” that normallywill exist. A method to create a single energy bubble in a highlymultipath environment is based on True Time Delay. Here, in place offixed relative phase shifts, the coherent transmissions from all PAPsare simultaneously ramped in frequency in a Frequency-ModulatedContinuous-Wave (FM-CW) manner, or in a Pseudo-Noise (PN)Frequency-Hopping (FH) manner. Alternatively, all Power Access Pointsare simultaneously phase modulated or Direct Sequence (DS) spread inphase. As with the relative phase shift of the unmodulated PAPs, timedelays of the modulation at each PAP will coherently combine to form anenergy “bubble” only at locations where the True Time Delays areidentical. This will greatly reduce the number of energy “bubbles”formed in a three-dimensional space, and hence will reduce (or evenremove) the connectivity map ambiguity.

The location of the isolated energy “bubble” is controlled by therelative start times of the FM-CW ramp (or PN code for FH and DSspreading) at each PAP. As this relative start time is changed, thelocation of the isolated energy “bubble” is moved in thethree-dimensional space. For each set of relative start times at thePAPs, the actual location of the isolated energy “bubble” is determinedfrom the responses of the “reference” locations. The difficulty with theuse of these ambiguity resolution techniques is that the bandwidthrequired (FM-CW ramp rate, FM hop rate) increases with the spatialresolution required. In most RFID tag location situations, this largebandwidth is not acceptable.

Second Method of Location Ambiguity Resolution:

Another method to resolving the location ambiguity of the energy“bubbles” is to separate the “bubbles” that are simultaneously formedinto distinct, separate groups while composing the connectivity map.This separation operation along with the “adjacent” group connectivityoperation will resolve most, if not all, location ambiguities. Alongwith the known locations of the reference energizable devices (or insome embodiments, the reference locations), a three-dimensional map ofthe location of all energizable devices in the three-dimensional space(e.g. warehouse) is generated.

First, beam-switching using the switched beam capability of the PAPswill separate the energy “bubbles” into subspaces. With each PAP havingN selectable beams in the horizontal (Azimuth) plane, the (warehouse)space can be easily subdivided into N² subspaces. Here, the power of tworeflects the number of spatial dimensions being covered, not the numberof PAPs being employed. If additionally, the vertical (elevation)coordinate is divided into M beams, then the space can be subdividedinto M x N² subspaces. With multiple PAPs contributing to the formationof energy “bubbles” within one subspace, the probability of havingmultiple ambiguous energy “bubbles” is greatly reduced.

With a large space (e.g. a warehouse), the total space can be dividedinto distinct regions, with each region being subdivided into N²subspaces. Not only will this limit the range from the Power AccessPoints to the receiving devices, it will provide faster operationthrough parallel processing.

Further refinement of the separation of the space into distinctsubspaces can be achieved. For energy “bubbles” that are substantiallyequidistant from all PAPs, the amplitudes of the signals from each PAPwill be approximately the same. This is not necessarily true for anenergy “bubble” that is near a single PAP, because it receives a majorportion of its energy from that PAP. As a result, multiple simultaneousenergy “bubbles” can be separated into multiple distinct groups, bysequentially switching off each of the PAPs, and observing whichenergizable device (e.g. RFID tag) responses “blink” on and off. Theterm “blink” as used herein means to shut off and return to the on-statewhen the PAP is switched back on. Alternatively or additionally, if areceiving device is enabled to return a Received Signal StrengthIndication (RSSI), a “blink” is determined as a substantial change inRSSI. Those that “blink” are close to the PAP that is turned off, andthose that do not “blink” are not. This procedure groups the multipleambiguous energy “bubbles” into P+1 subspaces in the warehouse space(where P is the number of Power Access Points), greatly reducing thelocation ambiguity.

In one embodiment, a refinement of this technique includessimultaneously switching off two adjacent PAPs. Here the energizabledevices that are located between the PAPs will “blink” on and off whilethe energizable devices that are far from the two PAPs will not. Thistechnique may be extended to three or more adjacent or separate PAPs.

The location ambiguity can be further refined in the area where no onePAP's power dominates the total received power (e.g., in the area notclose to any PAP). All energy “bubbles” are a product of the threedimensional standing wave pattern, and this standing wave pattern iscreated by the PAP's phases and the internal reflections of thewarehouse. The multiple energy “bubbles” in the area not close to anyPAP can be separated into subgroups by simultaneously rotating thepolarization of all PAPs. The energy “bubbles” that rely strongly on theinternal reflections of the warehouse will “blink” off, while those thatdo not rely strongly on the internal reflections will not. Ninety-degreepolarization rotation will create the largest distinction between thetwo groups of “bubbles”.

Several other values of polarization rotation can also be used toidentify different subgroups of energy “bubbles”, again by observingwhich energizable devices “blink” off and which do not. In addition tohelping to resolve the location ambiguity of the RFID tags, thissubgroup separation can also be used to help refine the connectivitymap, in a manner similar to the PAP's phase change procedure.

By use of these grouping techniques of the energizable devices, areceiving device connectivity map can be generated without ambiguity.With the use of the known locations of the reference tags, a threedimensional map of the physical location of all tags in the warehousecan be generated. The methods for determining the location ofenergizable devices are illustrated in FIG. 7.

Specifically, at 222 with all PAPs on, the space is separated intomultiple subspaces by selecting switched beam settings. At 224, thesubspace is further divided into multiple subgroups by sequentiallyturning off one or more PAPs. At 226, the subspace is further dividedinto multiple subgroups by switching the polarization of all the PAPs.In one embodiment, step 226 is performed after step 224. In anotherembodiment, one or more of steps 224 and 226 are performed concurrently.At 228, for each subspace, a connectivity map is constructed by movingan energy bubble through the subspace by changing the relative phases ofthe multiple PAPs. In another embodiment, step 228 is performed onsubgroups rather than subspaces. At 230, the connectivity map is fixed(determined) in space at multiple points using the known locations ofmultiple reference receivers, and the results of either the variousconnectivity maps from the plurality of subspaces or the plurality ofsubgroups.

At FIG. 8, a method for improved wireless energy transfer includessteering a first energy beam formed by a plurality of polarizers of aPAP at 250. At 252, the polarity of the first and a second energy beamare aligned at an energizable device.

At FIG. 9, a method for improved wireless energy transfer includessteering energy beams formed by PAPs to an energizable device at 260. At262, the polarity of each energy beam is aligned at the energizabledevice. At 264, a planar region is divided into subspaces. At 266, anenergy beam is scanned along a scan path within the subspace to detectan energizable device. At 268, a connectivity map is determined. At 270,the location of a receiving device and a neighboring device relative toa reference device is interpolated.

Additional Example Embodiments

The following are example embodiments, including at least someexplicitly enumerated as “ECs” (Example Combinations), providingadditional description of a variety of embodiment types in accordancewith the concepts described herein; these examples are not meant to bemutually exclusive, exhaustive, or restrictive; and the invention is notlimited to these example embodiments but rather encompasses all possiblemodifications and variations within the scope of the issued claims andtheir equivalents.

EC1: A method for energy beam optimization comprising:

receiving an energy beam at an energizable device from one of aplurality of PAPs, the energy beam having a plurality of transmittedphases including an initial transmitted phase during a first time slot,a second transmitted phase during a second time slot and a thirdtransmitted phase during a third time slot;

storing a received signal strength indication (RSSI) at the energizabledevice for each of the transmitted phases, when the received RSSIchanges by a threshold;

receiving at the PAP, each of the stored RSSI levels from theenergizable device; and

determining a received amplitude and a received phase of the energy beamat the energizable device for the initial transmitted phase by the PAP.

EC2: The method of EC1, wherein the second transmitted phase is shiftedby 90 degrees from the initial transmitted phase, and the thirdtransmitted phase is shifted by 180 degrees from the initial transmittedphase.

EC3: The method of EC1, wherein the second transmitted phase is shiftedby 180 degrees from the initial transmitted phase, and the thirdtransmitted phase is shifted by 270 degrees from the initial transmittedphase.

EC4: The method of EC1, further comprising adjusting the received phaseof the energy beam to be equal to a second received phase of a secondenergy beam transmitted by a second PAP.

EC5: A method for switched beam polarization alignment comprising:

steering a first energy beam towards a receiving device, the firstenergy beam transmitted by a plurality of antennae coupled to a PAP by aButler matrix; and

aligning at the receiving device, a first polarity of the first energybeam to a second polarity of a second energy beam transmitted by anotherPAP by combining at each of the plurality of antennae a first polarizedsignal derived from the PAP with a second polarized signal, the secondpolarized signal formed by rotating the first polarized signal.

EC6: An antenna system comprising:

a patch antenna including a dielectric substrate interposed between aresonant plate and a ground plate, the patch antenna including a firstfeed-point and a second feed-point;

a first variable gain amplifier (VGA) connected to the first feed-pointand configured to adjust a first amplitude of a signal;

a first phase shifter interposed between the signal and the first VGAand configured to adjust a phase of the signal; and

a second VGA connected to the second feed-point and configured to adjusta second amplitude of the signal, the patch antenna controlling a slantlinear polarization of the signal.

EC7: The system of EC6, wherein the phase is greater than or equal tozero degrees and less than or equal to 360 degrees.

EC8: A switched beam polarization alignment system comprising:

a four or more antenna systems, each antenna system comprising a patchantenna including a dielectric substrate interposed between a resonantplate and a ground plate, the patch antenna including a first feed-pointand a second feed-point, a first VGA connected to the first feed-pointand configured to adjust a first amplitude of a signal, a first phaseshifter interposed between the signal and the first VGA and configuredto adjust a phase of the signal, and a second VGA connected to thesecond feed-point and configured to adjust a second amplitude of thesignal, the patch antenna controlling a polarization of the signal;

a first cross-over device coupled to a first pair of the antennasystems;

a first pair of hybrid couplers coupled to the first cross-over deviceand a second pair of the antenna systems;

a second cross-over device coupled to the first pair of hybrid couplers;

a second pair of hybrid couplers coupled to the second cross-over deviceand the first pair of hybrid couplers;

a switch coupled to the second pair of hybrid couplers; and

a phase shifter coupled between an output of a power access point andthe switch.

EC9: A method for determining a receiver location comprising:

dividing a planar region including a plurality of devices into aplurality of subspaces, each subspace defined by a beam position from arespective one of a plurality of energy beams;

scanning the respective one of the energy beams along a scan path withinthe subspace to detect a presence of at least some of the plurality ofdevices by detecting a change in a received energy at each of the atleast some of the plurality of devices, the at least some of theplurality of devices including an energizable device, and one or more ofa neighbor device and a reference device, the reference device having apredetermined location within the planar region;

determining a connectivity map by finding a respective position for eachneighbor device relative to a position of the receiving device; and

interpolating a physical location of the receiving device and theneighbor device relative to the reference device.

EC10: The method of EC9 wherein the location of the receiving device isdetermined within one wavelength of the respective one of the energybeams.

EC11: The method of EC9 wherein each subspace is dividing into smallerspaces by sequentially deactivating one energy beam and detecting thepresence of a receiving device by a reduction in the received energy atthe receiving device.

EC12: The method of EC9 wherein each subspace is dividing into smallerspaces by sequentially deactivating two physically adjacent energy beamsand detecting the presence of a receiving device between the twophysically adjacent energy beams by a reduction in the received energyat the receiving device.

EC13: The method of EC9 wherein each subspace is dividing into smallerspaces by rotating a polarity of all of the energy beams and detectingthe presence of a receiving device by a reduction in the received energyat the receiving device.

EC14: Location determination and ambiguity resolution based onseparating the space to be covered into subspaces, generating aconnectivity map of multiple receivers within each subspace, and usingthe known locations of reference locations to establish known positionswithin the connectivity map.

EC15: The separation of the space into subspaces is achieved usingmultiple switched beam antennas to divide the area into N² subspaces inthe horizontal (Azimuth) plane where N is the number of beams availablein the horizontal plane from each PAP.

EC16: The separation of the space into subspaces can be extended intothe vertical (Elevation) coordinate with M vertical beams, resulting ina total number of subspaces in three dimensions of M×N²

EC17: The separation of the space into subspaces can be also increasedby sequentially turning off each PAP to separate the region intomultiple close and far subspaces.

EC18: The separation of the space into subspaces can be furtherincreased by sequentially turning off two or more, adjacent or separatedPAPs to separate the region into additional subspaces.

EC19: The separation of the space into multiple subspaces can also beincreased by sequentially employing orthogonal polarizations to separateclose but not adjacent receivers.

EC20: The separation of the space into multiple subspaces can be furtherincreased by sequentially employing other values of polarization toseparate close but not adjacent receivers.

EC21: The connectivity map is generated by selecting a subspace to beilluminated with the switched beam antennas, moving the energy bubblesthroughout the subspace by changing the relative phases of the multiplePAPs, and observing which receivers “blink” on and off when one or morePAPs are switched off, or when the polarization is rotated.

EC22: The connectivity map is fixed in space at multiple points throughthe known locations of the reference locations.

Although the invention is described herein with reference to specificembodiments, various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope of thepresent invention. Any benefits, advantages, or solutions to problemsthat are described herein with regard to specific embodiments are notintended to be construed as a critical, required, or essential featureor element of any or all the claims.

Unless stated otherwise, terms such as “first” and “second” are used toarbitrarily distinguish between the elements such terms describe. Thus,these terms are not necessarily intended to indicate temporal or otherprioritization of such elements.

What is claimed is:
 1. An apparatus for wireless energy transfer in amultipath environment comprising: a first one of a plurality of PowerAccess Points (PAPs) configured to transmit a first energy beam; asecond PAP configured to transmit a second energy beam; a reflected beamformed by the first energy beam reflected from a reflective surface,wherein the first energy beam constructively interferes with the secondenergy beam and the reflected beam to form at least one energy bubble;and a control module configured to sequentially change a location of theat least one energy bubble by adjusting a relative phase between thefirst energy beam and the second energy beam, wherein the location issequentially changed to a new location to cover a space including atleast one energizable device, and the energy bubble comprises an energylevel enabling the at least one energizable device to transmit a replysignal to the first PAP.
 2. The apparatus of claim 1 wherein the firstenergy beam and the second energy beam each comprise a respectiveomnidirectional pattern and two or more energy bubbles are formed. 3.The apparatus of claim 2 wherein two or more energizable devicescomprising different locations are concurrently energized by arespective each energy bubble.
 4. The apparatus of claim 1 wherein afirst phase of the first energy beam and a second phase of the reflectedbeam are aligned with the control module for an in-phase arrival at afirst one of the at least one energizable device.
 5. The apparatus ofclaim 1 wherein a first polarity of the first energy beam and a secondpolarity of the second energy beam are aligned with the control moduleto have a same polarity rotation at a first one of the at least oneenergizable device.
 6. The apparatus of claim 1 wherein the first energybeam has a first fundamental frequency equal to a second fundamentalfrequency of the second energy beam.
 7. The apparatus of claim 6 whereina first phase of the first energy beam, a second phase of the secondenergy beam, and a third phase of the reflected beam are aligned withthe control module for an in-phase arrival at a first one of the atleast one energizable device.
 8. The apparatus of claim 6 wherein afirst polarity of the first energy beam, a second polarity of the secondenergy beam, and a third polarity of the reflected beam are aligned withthe control module to have a same polarity rotation at a first one ofthe at least one energizable device.
 9. The apparatus of claim 1 whereinthe space is a three-dimensional space.
 10. The apparatus of claim 1wherein the space comprises a warehouse environment.
 11. A method forwireless energy transfer in a multipath environment comprising:transmitting a first energy beam with a first one of a plurality ofPower Access Points (PAPs); transmitting a second energy beam with asecond PAP; forming a reflected beam by the first energy beam reflectingfrom a reflective surface, wherein the first energy beam constructivelyinterferes with the second energy beam and the reflected beam to form atleast one energy bubble; and changing a location of the at least oneenergy bubble with a control module by adjusting a relative phasebetween the first energy beam and the second energy beam, wherein thelocation is sequentially changed to a new location to cover a spaceincluding at least one energizable device, and the energy bubblecomprises an energy level enabling the energizable device to transmit areply signal to the first PAP.
 12. The method of claim 11 furthercomprising energizing two or more energizable devices by a respectiveenergy bubble, wherein each of the two or more energizable devicescomprise a respective different location.
 13. The method of claim 11further comprising aligning for an in-phase arrival at a first one ofthe at least one energizable device, a first phase of the first energybeam and a second phase of the second energy beam.
 14. The method ofclaim 11 further comprising aligning to have a same polarity rotation ata first one of the at least one energizable device, a first polarity ofthe first energy beam and a second polarity of the second energy beam.15. The method of claim 11 further comprising aligning for an in-phasearrival at a first one of the at least one energizable device, a firstphase of the first energy beam, a second phase of the second energy beamand a third phase of the reflected beam.
 16. The method of claim 11further comprising aligning to have a same polarity rotation at a firstone of the at least one energizable device, a first polarity of thefirst energy beam, a second polarity of the second energy beam and athird polarity of the reflected beam.
 17. A method for wireless energytransfer in a multipath environment comprising: transmitting at firstenergy beam from a first Power Access Point (PAP) and a second energybeam from a second PAP; forming a reflected beam by the first energybeam reflecting from a reflective surface, wherein the first energy beamand the second energy beam constructively interferes with the reflectedbeam to form a plurality of energy bubbles, and each energy bubblecomprises an energy level configured to enable at least one energizabledevice to transmit a reply signal to the first PAP; receiving at thefirst PAP, a reply signal from at least one energizable device; andchanging a location of the at least one energy bubble with a controlmodule by adjusting a relative phase between the first energy beam andthe second energy beam, wherein the location is sequentially changed toa new location to cover a three-dimensional space including at least oneenergizable device.
 18. The method of claim 17 further comprisingenergizing two or more energizable devices by a respective energybubble, wherein each of the two or more energizable devices comprise arespective different location.
 19. The method of claim 18 wherein areceived energy level of the respective two or more energizable devicesis optimized by maximizing a minimum Received Signal Strength Indicationreceived at the first PAP from each of the energizable devices.
 20. Themethod of claim 18 wherein the received energy level is optimized usinga phasor decomposition method.